Definition

Stretching is a form of physical activity where muscles are extended into a position beyond their resting length for the purpose of increasing flexibility of muscles and overall range of motion (ROM) in joints in order to enhance overall physical performance and reduce the risk of injuries.[1]

Flexibility

Flexibility varies from person to person. Though within an individual, flexibility can vary significantly between one joint of the body compared to another. It is known that females generally have greater flexibility than males.[2] Flexibility is maintained by doing regular physical activity and specific stretching exercises. Conditions such as ankylosis (pathological loss of ROM) and hypermobility (excessive ROM) exist.[1]

Types of Stretching

Passive Static

Static stretching is where the person stretches a target muscle group by holding themselves in a position which would extend the muscle.

This can be done alone or with the assistance of a partner. If the stretching exercise is done individually, one could either hold themselves in a stretched position (for example, to stretch the hamstrings; while in a seated position, straighten the legs and bring the head towards the knee without bending the leg). To make this easier, one can hold their foot to pull themselves toward the knee. If the person cannot touch their toes, they can wrap a towel around their foot and pull themselves into the stretch via the towel instead. An easier way to do passive static stretches is to find a partner. For the same stretch just described, a partner can help push the person stretching towards their target. Essentially, the person stretching relaxes his/her body entirely and allows the partner to physically manipulate their body into positions for a stretch in the target muscle. The stretch should be held at a position of mild discomfort for adaptation to take place.

The duration of how long a static stretch should be held is an open topic for discussion as various durations have been suggested by different sources. This may include holding a stretch for a short period of time varying between 15-30 seconds,[1] or holding a stretch for up to 1 minute.[3] Research on the effect of duration of stretches on ROM have suggested that the key to gaining flexibility is about the total time spent on stretching overall rather than the amount of time spent holding a single stretch.[4] As such it could be assumed that doing 4 separate stretches lasting 15 seconds each is just as effective as holding a single stretch which lasts 1 minute to reap benefits. The key is to feel stress relaxation or reduction of passive tension in the target muscle group. If this is achieved, a more intense stretch can be performed thereafter to gradually increase flexibility.

Active Static

Active Static stretching, similar to passive static stretching is when the target muscle group is held in an extended position. However, unlike passive static stretching which uses assistance from other sources to hold the body in place, active static stretching is done using the strength of the agonist muscle group.[3]

Using the example of a hamstring stretch; if a person is to do an active static version of a hamstring stretch, he or she would stand on one leg and raise the target leg up close to their face and hold it in the air (seemingly like a high kick paused in motion). This type of stretching is commonly seen in exercises such as yoga and pilates.

Ballistic (Dynamic)

Ballistic stretching is where the target muscle group is stretched through movement. The stretch is facilitated by momentum. An example would be a straight leg swing forwards and backwards which would stretch the quadriceps, hamstrings, hip flexors and extensors.

Essentially, dynamic stretching does not keep the limbs in a stationary position. The stretch of the target muscle group is gained through “bouncing” movements which gradually eases against the stiffness of tense muscles.[3] It is recommended that this type of stretching is done in a mild pace as a warm up to avoid imposing excessive forces on the muscles. It is assumed that static flexibility is maintained through regular physical activity in this way.[1]

Proprioceptive Neuromuscular Facilitation (PNF)

PNF stretching is a particular routine which utilizes the inhibitory effects of the golgi tendon organs.[1] PNF is done by first performing an isometric muscle contraction with the target muscle followed by a passive static stretch afterwards. The isometric contraction activates the golgi tendon reflex which is a protective feedback mechanism that triggers when high tension caused by voluntary contraction is detected within the muscle tendon.[5] The reflex causes relaxation of the active muscle which facilitates a greater passive static stretch that follows in the PNF routine.

Again using the hamstring stretch as an example; the person stretching would lie supine (backside down) on the floor. For the first step, they would raise their target leg up pointing towards the sky. They would then perform an isometric contraction with their hamstrings (attempting to push their leg down to ground level against a stationary resistance like wall or an assistant). After holding the contraction for a while, they would relax and perform a passive static hamstring stretch alone or with the assistance of a partner.

Benefits of Stretching

Consistently following a series of stretching protocol for each muscle group can increase their flexibility and in turn provide a greater ROM.[6]

Flexibility is lost as the body ages if no intervention is carried out. Additionally, inactivity also contributes to reducing flexibility which is a cause for concern as a significant portion of the population nowadays work in inactive office jobs for long hours. As an example; women who wear high heeled shoes on a regular basis gradually develop decreases in ankle flexibility and also get tight calf muscles as the ankles become accustomed to a plantarflexed position.[7] In which case, these women have a greater chance of straining their calves when they return to wearing trainers where they stand flat on the ground because their calves will be in a relatively stretched position compared to what they have become accustomed to.

As such, even populations which are not concerned with athletic performance should implement a stretching program into their daily lives to allow the body to maintain a normal range of movement necessary for everyday life.

Detriments of Stretching

While stretching is important to an extent to develop muscle flexibility, research on populations of either ends of the spectrum with regards to flexibility have been shown to correlate with higher risks of musculoskeletal injuries.[8]

Extremely inflexible individuals are more susceptible to muscle strain injury when stiff muscles are forced into lengths they are not accustomed to which happens often under excessive loads of weight or forces.

On the other hand, extremely flexible individuals, while they reap the benefits of a greater ROM than the average population, the flexible muscles provide less tissue resistance at each joint and thus contributes to greater joint instability.[1]

The message to acknowledge here is that stretching should not be taken to an extent which stresses the body beyond a normal ROM. Together with a stretching program, other activities including high impact exercises and resistance training should be incorporated in combination to reap maximal benefits for the body.

When to stretch?

Stretching can be done at any time by itself, before or after exercise. However, there are various opinions regarding when particular types of stretching would be more suitable than the others.

An existing idea is that stretching during a cooldown period after exercise is more appropriate than as a warm up for four reasons:[1]

Warmed-up muscle tissues are less likely to be injured.

Stretching within a workout does not produce gains in static flexibility.

Stretching prior to a workout generally has no effect in reducing immediate risk of muscle injuries in the workout.

There are controversies regarding when particular methods of stretching are more effective than others. A study examining the different effects of dynamic stretching against static stretching as a warm up for performance in sprinting and jumping for elite youth soccer players concluded that dynamic stretching produced greater performance in comparison to static stretching.[9] The explanation behind the observed phenomenon is that while static stretching increases short term ROM, a simultaneous decrease in passive tension is also observed thereby decreasing effective contractile forces. This effect may last 30-60 minutes.

On the other hand, there are studies which concluded that static stretching causes insignificant effect on performance. Studies on the effects of static stretching and PNF stretching in youth soccer players suggested that it in fact does not cause acute decreases in sprint speed and agility.[10][11]

To summarize, it is generally a good idea to perform dynamic stretches of mild intensity as part of a warm up for neural activation of the muscles before exercise. While static or PNF stretching should be done as a cooldown for increases in flexibility. Stretching should be done as often as possible for effects to take place therefore it should be introduced to the youth at an early age so that they can learn the concept and build a habit of it in their life as they grow up.

Passive Stretching as Treatment in Infants with Congenital Disorders

Passive stretching has been used as a type of therapy for infants who are born with some congenital conditions including:

Congenital muscular torticollis;[13] an abnormal, asymmetrical head or neck position.

Camptodactyly;[14] a condition where one or more fingers are in a permanently flexed position at the interphalangeal joints.

In all the congenital conditions, a combination of passive stretching and splinting at the joints helped facilitate joint mobility or correction of joint angles in infants 36 months and younger. Follow up periods which lasted a duration of no less than 1 year after intervention have shown that passive stretching on infants is actually a safe procedure which can help significantly increase their quality of life via increasing effective body function.